Modern drilling techniques for oil and gas wells have become very sophisticated in recent years. Original equipment involved only the bit on the end of a drill string composed of lengths of drill pipe having a hollow core through which fluids such as drilling mud could be circulated to remove cuttings. As techniques developed, certain down hole equipment was designed to improve the performance of such drills. For instance, stabilizers are used to maintain proper alignment of the drill string so as to prevent deviation or to change the direction of a hole.
In some cases, the rotary drilling function is performed by a down hole motor at the bottom of the drill string activated by the flow of fluid. These devices require "dump subs" to allow the drilling fluid to be bypassed when the pipe is being withdrawn so that mud is not spilled at the top of the string.
Other devices used include down hole packers, blowout preventers and mud hammers which use vibratory force to increase the efficiency of the drilling operation.
Many of these devices need to be activated at certain times, depending on the circumstances, while they are in the hole. In other cases, the devices need to be deactivated to run them into the hole and activated once they are in position, or deactivated in order to withdraw them from the hole. Since many holes are deep and time is costly, it is always an undesirable expense to withdraw this equipment from the hole when it needs to be adjusted.
Thus, it is important to develop mechanisms by which down hole devices such as stabilizers, packers, etc. may be engaged or disengaged by operations which can be conducted on the drill floor.
Some of these devices are operated by using the blocks supporting the drill string to change the weight which is applied to the bottom of the drill string at the bottom of the hole. Other devices have been developed which operate by changing the pressure applied to the fluid which is circulated through the drill string in order to activate or deactivate the device.
Many of these devices are difficult to operate because changing weight or pressure will activate or deactivate them at an inappropriate time. Some devices are difficult to operate because it is not easy to determine the weight or pressure which is being applied at the bottom of the drill string. Others require that the conditions for activation of the device remain relatively constant and these conditions may not be ideal for carrying on the drilling operation.